1. Field of the Invention
The present invention relates to a cold fumeless carbon mixture suitable for ramming of alumina reduction cell cathode seams and sidewalls, the linings of carbon-lined crucibles and the patching of same, and a method for producing such mixtures.
2. Discussion of the Prior Art
In the conventional practice of producing aluminum metal by the electrolytic reduction of alumina in a cell, the cathode of the cell is a large tank lined with carbon. Carbon blocks with steel electrodes embedded in them form the bottom of this cell and are spaced uniformly so that approximately 2-inches is provided between each block for ramming a seam. These blocks provide higher strength, higher density and lower porosity and resistance than a continuous (monolithic) rammed paste lining. The blocks are formed into a liquid tight container surface by filling the joints between the blocks with a rammed carbonaceous cement. In conventional practice this cement is made up of a graded aggregate of calcined anthracite with a mixture of coal tar pitch having a softening point of about 75.degree. C. This mix is heated to a consistency such that the mix can be rammed into the joints between the cathode blocks. At the temperature of mixing (about 150.degree. C.) and the temperature of installation (about 130.degree. C.), this mixture fumes and steams badly providing an extremely undesirable working atmosphere with a fume that is a skin, lung and eye irritant. The material must be worked over a very limited temperature range, because when too cold the mixture does not compact satisfactorily and breaks up and crumbles when it is tamped in the joint between the cathode blocks. Considerable coordination is needed to insure delivery of the mix at a proper temperature and to provide adequate labor to ram the mix before it cools and becomes unworkable.
Present manufacturing practices require unnecessary expenditure of energy in holding the binder pitch in liquid storage and in providing heat to the mixture to warm the aggregate material and blend the materials to a proper consistency. This mixing time is usually 30 minutes to an hour, depending on the capacity of the heating system to the mixer. The mix must usually be used within an hour of manufacture or it becomes chilled and unworkable.
Attempts have been made over the year to improve the seam ramming mix, for example Dell (U.S. Pat. No. 3,576,700) and Reamey (U.S. Pat. No. 3,871,986 and U.S. Pat. No. 3,952,092) patented systems for improving the lining practice and developing advantageous substitutes for coal tar pitch. More recently, Dell, (U.S. Pat. No. 4,167,419) patented a mix for reducing the ramming temperature by including a solvent that lowered the softening point of the pitch to produce a mix capable of being tamped without the application of heat. French patent applications (FR No. 7,812,447 and FR No. 7,904,769) were published by D. Dumas (Savoy) for a cold carbon paste for sealing reduction cell linings where the low temperature plasticizer is a carbohydrate such as molasses and the permanent binder is a high softening point pitch. Other proposed binder systems have included such materials as furfural resins.